In North America, approximately 25% of human immunodeficiency virus (HIV) cases are attributable to injection drug use. Illicit drug users (DU) as a whole represent some of North America's most vulnerable populations and include a disproportionate number of women, sex trade workers, ethnic minorities, street involved persons and the homeless. DU with HIV who start and remain on successful treatment are less likely to become ill or die, and also are less likely to pass the infection on to their sexual and drug using partners. Unfortunately, DU are less likely than non-DU to start HIV treatment, and if they do start, they are less likely to stay on it. One possible strategy to address this problem is to provide DU with money as an incentive for starting HIV treatment and for taking it regularly over a period of time to ensure treatment success. Such incentives have been used successfully to reinforce desired behaviors in other fields such as weight management. The proposed research seeks to assess the effectiveness of monetary reinforcers in engaging and retaining HIV-infected DU in HIV treatment programs. First, 300 DU found through outreach will be randomly assigned to receive (150) or not (150) a gift card for participating in the screening process that determines whether they are eligible for HIV treatment, including a clinic visit with laboratory testing ($10) and a return clinic visit to receive the results ($40). The aim of this part is to see whether the DU offered the reinforcer will be more likely to complete the screening process. Next, 240 DU who are eligible to start HIV treatment will be assigned to either receive (160) or not (80) a small monetary reinforcer for the first year while taking treatment. For the first 6 months, study participants assigned to the intervention arm will receive a small monetary reinforcer (starting at $10 and increasing to $25) at the end of each monthly clinic visit that they attend. For the next 6 months, when they attend clinic visits AND their blood tests determine that the treatment is being taken regularly and is successful, they will receive a reinforcer (which will be variable based on a "fishbowl prize draw" system). Finally, they will be seen after another 6 months on treatment, to see if receiving reinforcers during the first year makes them more likely to still be taking successful HIV treatment 6 months later. All study participants will receive standard medical treatment for HIV. PUBLIC HEALTH RELEVANCE: It is critical that drug users become a focus of HIV care in order to reduce the rates of HIV- related illness and death in this group, and also to decrease the risk of HIV transmission to their sexual and drug using partners. Financial reinforcers may increase recruitment of this population into HIV treatment and lead to higher rates of long-term retention and treatment success at a reasonable cost. The scientific evaluation of this intervention strategy will be of value to health policy-makers throughout the world.